The present invention relates to a component for insert casting, which is enveloped in a casting metal through insert casting, and a cylinder block having such an insert casting component as a cylinder liner.
Components for insert casting include, for example, cylinder liners, which are integrated with a cylinder block through insert casting to form cylinder bores. To maintain a high level of roundness of a cylinder bore, the outer circumferential surface of such a component, which contacts the casting material used in insert casting, needs to have a great bond strength with the cylinder block.
To produce such a great bond strength, it is important to adjust the state of the cylinder liner outer circumferential surface. Accordingly, a technique has been proposed in which a sprayed layer covers a cylinder liner outer circumferential surface to form a surface layer (for example, Japanese Laid-Open Utility Model Publication No. 53-163405). Japanese Laid-Open Utility Model Publication No. 53-163405 discloses a surface layer on a cylinder liner outer circumferential surface onto which granulated metal is sprayed such that the granulated metal irregularly collects on the surface and forms asperities. During casting, molten metal flows into the recesses of the asperities to produce anchor effect, and a great bond strength is produced.
Further, there has been proposed a technique in which a film of a low melting point material is metallurgically bonded to a cylinder liner outer circumferential surface by shot peening process or plasma spraying, so that no oxide film is formed on the surface (for example, Japanese Laid-Open Patent Publication No. 2003-53508). This increases the adhesion between the cylinder liner and a cylinder block.
Another technique has been proposed in which an activation layer made of an aluminum alloy is formed as a surface layer in a top dead center region and a bottom dead center region of a cylinder liner outer circumferential surface, so that the activation layer establishes metallic bonding with a crankcase (for example, Japanese Laid Open Patent Publication No. 2003-120414).
With the recent trend of reducing the weight of internal combustion engines, designs of engines with short distances between the cylinder bores have been adopted. Also, there is trend for increasing the power of engines. Accordingly, in a cylinder block produced through insert casing of a cylinder liner, there is a demand for improving the adhesion between the cylinder liner and the cylinder block, thereby improving the cooling performance.
However, in Japanese Laid-Open Utility Model Publication No. 53-163405 and Japanese Laid Open Patent Publication No. 2003-120414, the sprayed layer on the cylinder liner outer circumferential surface is formed by causing metal particles, which have been melted at a high temperature, to collide with the cylinder liner. Therefore, an oxide film is formed on the surface of the sprayed layer, and oxides exist in the sprayed layer. As a result, the thermal conductivity of the metal after the spraying process becomes less than that of the same metal before the process. This configuration does not improve the cooling performance to a satisfactory level.
According to Japanese Laid-Open Patent Publication No. 2003-53508, a film of a low melting point material is formed on a cylinder liner outer circumferential surface. When the film contacts molten metal during casting, thermal effect causes fusion, so that a favorable metallic bonding is produced. However, as in Japanese Laid-Open Utility Model Publication No. 53-163405 and Japanese Laid Open Patent Publication No. 2003-120414, the film is formed in a high temperature molten state such as spraying. Thus, formation of oxide film on the surface and formation of oxide layers in the film are inevitable. Therefore, this configuration does not guarantee a satisfactory level of cooling performance. In Japanese Laid-open Patent Publication No. 2003-53508, shot peening is used. However, shot peening is a surface treatment method and cannot form a complete film.